Method of producing a multicolor LED display

ABSTRACT

A method produces a multicolor LED display, the display including an LED luminous unit having a multiplicity of pixels. First subpixels, second subpixel and third subpixels contain an LED chip that emits radiation of a first color, wherein a first conversion layer that converts the radiation into a second color is arranged at least above the second subpixels and a second conversion layer that converts the radiation into a third color is arranged above the third subpixels. At least one process step is carried out in which the first or second conversion layer is applied or removed in at least one defined region above the pixels, wherein a portion of the LED chips is electrically operated, and wherein the region is defined by the radiation generated by the operated LED chips, generated heat or a generated electric field.

TECHNICAL FIELD

This disclosure relates to a method of producing a multicolor LEDdisplay in which light of a plurality of colors is generated usingconversion layers.

BACKGROUND

A multicolor LED display can be realized, for example, by virtue of thefact that the pixels of the LED display in each case containblue-emitting LED chips, wherein a first conversion layer is applied toa first portion of the pixels, the first conversion layer converting theblue light into green light, and a second conversion layer is applied toa second portion of the pixels, the second conversion layer convertingthe blue light into red light. Alternatively, it is also possible forboth a first conversion layer and a second conversion layer to beapplied to the second portion of the pixels to convert the blue lightinto green light by the first conversion layer and to convert the greenlight into red light by the second conversion layer.

In this way, an RGB display can be realized with a multiplicity ofblue-emitting LED chips using two conversion layers.

Suitable conversion substances to convert blue light into green light orblue and/or green light into red light are known per se. The conversionlayers containing the conversion substance can be selectively applied tothe LED chips, for example, in the form of laminae. However, this isvery complex in particular for LED displays comprising two differentconversion substances. This method is suitable for LED displays in whichthe pixels have an edge length of more than 100 μm. A considerableadjustment outlay arises, however, in the case of smaller pixel sizes.

It could therefore be helpful to provide a method of producing amulticolor LED display in which pixels of different colors are producedwith a comparatively low production and adjustment outlay, wherein themethod is suitable in particular for LED displays having very smallpixel sizes.

SUMMARY

We provide a method of producing a multicolor LED display including anLED luminous unit having a multiplicity of pixels, wherein the pixelsinclude first subpixels that emit a first color, second subpixels thatemit a second color and third subpixels that emit a third color; thesubpixels contain an LED chip that emits radiation of the first color; afirst conversion layer that converts radiation of the first color intoradiation of the second color is arranged at least above the secondsubpixels; and a second conversion layer that converts radiation of thefirst color and/or the radiation of the second color into radiation ofthe third color is arranged above the third subpixels; includingimplementing at least one process step in which the first conversionlayer or the second conversion layer is applied or removed in at leastone defined region above the pixels to arrange the first conversionlayer above the second subpixels and arrange the second conversion layerabove the third subpixels; a portion of the LED chips electricallyoperating in the process steps; and defining at least one region byelectromagnetic radiation generated by the portion of the LED chips,generated heat or a generated electric field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F show a schematic illustration of the method in accordancewith one example on the basis of intermediate steps.

FIGS. 2A to 2F show a schematic illustration of the method in accordancewith a further example on the basis of intermediate steps.

FIGS. 3A to 3F show a schematic illustration of the method in accordancewith a further example on the basis of intermediate steps.

FIGS. 4A to 4E show a schematic illustration of the method in accordancewith a further example on the basis of intermediate steps.

FIGS. 5A to 5H show a schematic illustration of the method in accordancewith a further example on the basis of intermediate steps.

FIGS. 6A to 6F show a schematic illustration of the method in accordancewith a further example on the basis of intermediate steps.

FIGS. 7A to 7J show a schematic illustration of the method in accordancewith a further example on the basis of intermediate steps.

FIGS. 8A to 8I show a schematic illustration of the method in accordancewith a further example on the basis of intermediate steps.

FIG. 9 shows a schematic illustration of the method in accordance with afurther example on the basis of an intermediate step.

FIG. 10 shows a schematic illustration of the method in accordance witha further example on the basis of an intermediate step.

DETAILED DESCRIPTION

We provide a method of producing a multicolor LED display wherein theLED display comprises an LED luminous unit having a multiplicity ofpixels. The pixels preferably comprise first subpixels that emit a firstcolor, second subpixels that emit a second color and third subpixelsthat emit a third color. Preferably, the first subpixels emit bluelight, the second subpixels emit green light, and the third subpixelsemit red light. In particular, the pixels can in each case form a pixelof an RGB LED display.

The subpixels in each case contain an LED chip that emits radiation ofthe first color. The LED display can contain in particular LED chipsbased on a nitride compound semiconductor and emit blue light, forexample. Preferably, all the LED chips of the LED display emit the lightof the first color, in particular blue light. The multicolor nature isadvantageously produced in the LED display by a first and/or a secondconversion layer arranged on a portion of the subpixels.

In particular, in the method, a first conversion layer that convertsradiation of the first color into radiation of the second color isarranged at least above the second subpixels. The first conversion layercan be suitable, for example, to convert blue light emitted by the LEDchips into green light.

Furthermore, a second conversion layer that converts radiation of thefirst color and/or the radiation of the second color into radiation of athird color is advantageously arranged above the third subpixels. Thesecond conversion layer can, for example, convert blue light emitted bythe LED chips into red light. In this case, the second conversion layeris advantageously arranged directly above the LED chips of the thirdsubpixels which emit blue light.

Alternatively, however, it is also possible for the second conversionlayer to be arranged regionally above the first conversion layer toconvert the radiation of the second color into radiation of the thirdcolor. By way of example, the second conversion layer can convert greenlight generated by the first conversion layer into red light. In thiscase, the third subpixels of the LED display that, for example, emit redlight, have both the first conversion layer and the second conversionlayer arranged thereabove.

In one configuration of the method, advantageously, no conversion layeris arranged above the first subpixels. The first subpixels thereforeemit the unconverted light emitted directly by the LED chips, forexample, blue light. Alternatively, however, it would also be possiblefor a further conversion layer to be arranged above the first subpixels.By way of example, it is possible to use LED chips which emit in the UVspectral range and whose emitted UV light is converted into blue, greenand red light by three different conversion layers.

The multicolor LED display need not necessarily be an RGB display, butrather can in particular also have more than three colors. By way ofexample, in addition to the colors red, green and blue, the multicolorLED display can emit at least one further color such as, for example,yellow light in an RYGB display.

In the method, to arrange the first conversion layer above the secondsubpixels and arrange the second conversion layer above the thirdsubpixels in each case at least one process step is carried out in whichthe first conversion layer or the second conversion layer is applied toat least one defined region above the pixels or is removed form adefined region above the pixels. In this process step, advantageously, aportion of the LED chips is electrically operated. The at least onedefined region to which the first or second conversion layer is appliedor from which the first or second conversion layer is removed isadvantageously defined by electromagnetic radiation generated by theelectrically operated portion of the LED chips, generated heat or agenerated electric field.

The method advantageously uses an operative variable generated duringthe operation of a portion of the LED chips, in particular the generatedradiation, the generated heat or the generated electric field to enablethe first and/or second conversion layer to be selectively applied tothe subpixels or selectively removed from the subpixels. Since theregion to which the first and/or second conversion layer is applied orfrom which it is removed is defined by operation of a portion of the LEDchips, the adjustment outlay in the method is advantageously low. Inparticular, a step of applying and adjusting a mask can be obviated withthe method. The method is therefore particularly advantageous for LEDdisplays having very small pixels in which a considerable adjustmentoutlay would arise when applying conversion layers using a mask method.

In one configuration of the method, the first conversion layer isarranged above the LED luminous unit and the second conversion layer isarranged above the first conversion layer. In particular, first thefirst conversion layer can be arranged over the whole area on the LEDluminous unit and the second conversion layer can be arranged over thewhole area on the first conversion layer.

The first and second conversion layers can be applied successively, forexample. Alternatively, the first and second conversion layers can beapplied to the LED luminous unit simultaneously, for example, in theform of a prefabricated two-layered converter lamina. The converterlamina can comprise, for example, the first conversion layer whichcontains a first conversion substance, and a second conversion layerwhich contains a second conversion substance and connects to the firstconversion layer.

In one configuration, the second conversion layer is removed from thefirst subpixels and the second subpixels. Furthermore, the firstconversion layer is removed from the first subpixels.

In this way, both the first and the second conversion layers are removedfrom the first subpixels. The first subpixels therefore emit theunconverted light of the first color, for example, blue light. Sinceonly the second conversion layer is removed from the second subpixels,the second subpixels emit the light of the second color generated by thefirst conversion layer, for example, green light. Neither the first northe second conversion layer is removed from the third subpixels suchthat the latter emit the light of the third color, for example, redlight.

In one configuration, the removal of the first and/or second conversionlayer is effected by a method of local layer removal. The method oflocal layer removal is preferably controlled by a spectrally sensitiveoptical recognition of the radiation emitted by a portion of the LEDchips. The method of local layer removal can be in particular laserablation or an etching process, preferably a wet-chemical etchingprocess.

The method can be performed, for example, such that after the first andsecond conversion layers have been applied over the whole area, only thefirst and second subpixels are switched on, which are luminous with thethird color, in particular red, on account of the conversion layersapplied above them. The luminous image thus generated can be recordedspectrally sensitively by optical image recognition, for example, and inthis way a laser beam can be controlled such that it ablates the redluminous regions of the conversion layers until emission of light in thegreen spectral range is predominant in these regions. Preferably, thewavelength of the laser used for the laser ablation is chosen such thatthe absorption takes place only in the second conversion layer.

In a further process step, the first subpixels from which the firstconversion layer is also intended to be removed are then switched on.These pixels are luminous with the second color, in particular green, onaccount of the first conversion layer still present. By laser ablationwith a wavelength which preferably leads to a selective absorption inthe first conversion layer, the first conversion layer is then locallyremoved until the switched-on first subpixels predominantly emit lightof the first color, in particular blue. The selective removal of thefirst and/or second conversion layer by laser ablation canadvantageously be effected more rapidly and more precisely than, forexample, the application of microstructured converter laminae.

In another configuration of the method, a wet-chemical etchant islocally applied above a portion of the subpixels from which the firstand/or second conversion layer are/is intended to be removed, forexample, by an inkjet method. During application, adjustment ispreferably effected by an optical image recognition method involvingdetection of the light from the LED chips of the respective subpixels.Consequently, the radiation emitted by a portion of the LED chips isutilized to adjust the local application of the etchant.

In a further configuration of the method, the removal of the firstand/or second conversion layer is effected by a method for local layerremoval advantageously controlled by heat emitted by a portion of theLED chips and/or by emitted electromagnetic radiation. In this case,removal of the first and/or second conversion layer can be effected inparticular by a wet-chemical etching method. For this purpose, awet-chemical etchant whose etching rate at room temperature or in acooled environment is negligible is preferably selected. After theetchant has been applied, the LED chips of the subpixels from which thefirst and/or second conversion layer are/is intended to be removed areswitched on, as a result of which local heating of the etchant andadditionally media transport through convection commence. This leads toa locally greatly increasing etching rate, as a result of which it ispossible to obtain a locally delimited removal of the first and/orsecond conversion layer in the region of the LED chips which areelectrically operated.

In a further advantageous configuration of the method, removal of thefirst and/or second conversion layer is effected by a method for locallayer removal advantageously locally amplified by the electric fieldgenerated by a portion of the LED chips. In this configuration, theremoval of the first and/or second conversion layer is preferablyeffected by a dry etching method. This variant of the method implementsa locally amplified etching of the first and/or second conversion layerin the region of the LED chips of the subpixels which are operated. Thelocally increased etching rate is based on the influencing of the ionsgenerated during the dry etching process by the electric field of theLED chips. Furthermore, the etching rate of the dry etching process canincrease locally as a result of the heat generated by the LED chips.

The above-described variants of the method advantageously in each caseuse a method for local layer removal, wherein preferably in a firstprocess step, first the first and second subpixels are operated toremove the second conversion layer from these subpixels and, afterward,only the first subpixels are operated also to remove the firstconversion layer from the first subpixels. In this way, the first and/orthe second conversion layer are/is locally removed in defined regionsmarked by the radiation generated by a portion of the LED chips, thegenerated heat or the generated electric field.

In further configurations of the method described below, the firstand/or the second conversion layer are/is locally applied in definedregions marked by the radiation emitted by a portion of the LED chips,by the heat emitted by a portion of the LED chips or by the electricfield generated by a portion of the LED chips.

In one configuration of the method, a radiation- and/or heat-sensitivelayer is applied and altered in regions by the radiation emitted by theportion of the LED chips and/or by the generated heat. In the regionsaltered by the emitted radiation and/or the generated heat or outsidethe altered regions, openings are subsequently produced in theradiation- and/or heat-sensitive layer.

In one configuration, the radiation- and/or heat-sensitive layer is aphotoresist layer, wherein the photoresist layer is exposed in theregions by the electromagnetic radiation emitted by the portion of theLED chips.

By way of example, a photoresist layer is applied and exposed by theradiation emitted by a portion of the LED chips. Afterward, thephotoresist layer is developed and in this way openings are produced atthe exposed locations or alternatively at the non-exposed locations.This process can analogously also be brought about by the heat arisinglocally during operation of a portion of the LED chips or by aninteraction of the emitted electromagnetic radiation and the emittedheat, if a heat-sensitive polymer is used as the photoresist layer orinstead of the photoresist layer.

The photoresist layer can be a positive resist layer or a negativeresist layer. In the positive resist layer, openings are produced at theexposed locations during the development step. By operation of a portionof the subpixels during exposure, therefore, openings can be selectivelyproduced above a desired portion of the subpixels. In an alternative useof a negative resist layer, openings are produced at the non-exposedlocations, with the result that, by the operation of a portion of thesubpixels during exposure, openings can be selectively produced abovethe non-operated LED chips.

In one configuration of the method, the photoresist layer advantageouslycontains no conversion substance. It is indeed possible to introduce aconversion substance into the photoresist layer and directly structurethe photoresist layer functioning as a conversion layer in this case byexposure with the LED chips. However, we found that a conversion layerin which the conversion substance is embedded into a resist layer canbecome brittle or yellow under the action of light. In the method,therefore, advantageously the first and/or the second conversion layerare/is applied in each case in openings of a photoresist layer and thephotoresist layer is completely removed again in each case by lift-offtechnology.

In a further configuration, the radiation- and/or heat-sensitive layeris a heat-sensitive layer, wherein the heat-sensitive layer is alteredin regions by heat generated by a portion of the LED chips. Theheat-sensitive layer can be decomposed, for example, by the heatgenerated by the LED chips such that it can be selectively removed inthe heated regions in order to produce the openings. In a manner similarto that in a positive photoresist layer, the heat-sensitive layer isremoved in the regions altered by the generated heat. Alternatively, theheat-sensitive layer can comprise, for example, a polymer selectivelycured by the generated heat, wherein the heat-sensitive layer issubsequently removed to produce the openings in the non-cured regions.In a manner similar to that in a negative photoresist layer, theheat-sensitive layer in this case is removed outside the regions alteredby the generated heat.

In one configuration of the method, a radiation-absorbing layer isapplied before the heat-sensitive layer is applied. Theradiation-absorbing layer preferably converts the radiation emitted bythe LED chips into heat. In this way, local heating of theheat-sensitive layer is advantageously amplified in the region of theelectrically operated LED chips. The radiation-absorbing layer isadvantageously removed again in one of the subsequent method steps.

In one configuration, the first conversion layer or the secondconversion layer is applied to the radiation- and/or heat-sensitivelayer and removed again outside the openings by lift-off technology.

By way of example, in one method step, the first conversion layer isapplied to the radiation- and/or heat-sensitive layer, for example, inthe form of a paste containing a first conversion substance. The firstconversion layer fills, in particular, the openings produced beforehand.Outside the openings, the conversion layer is removed again by lift-offtechnology together with the radiation- and/or heat-sensitive layer, forexample, a photoresist layer.

In a further step, a second radiation- and/or heat-sensitive layer, forexample, a second photoresist layer, is preferably applied. Analogouslyto the procedure in the previously applied radiation- and/orheat-sensitive layer, openings are subsequently produced in the secondradiation- and/or heat-sensitive layer. Subsequently, the secondconversion layer is applied and removed again outside of the openings bylift-off technology.

The method steps explained in association with the first conversionlayer are therefore repeated to selectively apply the second conversionlayer. After removal of the first and/or second radiation- and/orheat-sensitive layer, the first and/or second conversion layer can ineach case be baked for stabilization.

In a further configuration of the method, the radiation- and/orheat-sensitive layer is applied to the first conversion layer or to thesecond conversion layer. The first conversion layer or the secondconversion layer is removed after the production of the openings in theradiation- and/or heat-sensitive layer in the openings by a method forlayer removal. The method for layer removal is preferably an etchingprocess which can be, for example, a wet-chemical etching process or adry etching process.

In a further configuration of the method, the first and/or the secondconversion layer are/is selectively deposited onto a portion of thesubpixels. In this configuration, the first and/or the second conversionlayer are/is deposited by electrophoresis, wherein the deposition islocally amplified by the electric field generated by a portion of theLED chips.

In this variant, selective application of the first and/or secondconversion layer is effected, for example, by a conversion substance ofthe first or second conversion layer being applied in a dispersion. TheLED chips of the subpixels to which the first or second conversion layeris intended to be applied in the process step are then electricallyoperated. On account of the electric field that arises during operationof the LED chips, the conversion substance in the dispersion istransported to the switched-on subpixels. In this way, the first and/orsecond conversion layer are/is deposited in a targeted manner above thesubpixels whose LED chips are operated during the electrophoreticdeposition.

Subsequently, a drying and/or baking step is preferably carried out. Theelectrophoretic deposition is preferably carried out successively forthe first conversion layer and the second conversion layer. In theelectrophoretic deposition of the first and/or second conversion layer,the thickness of the deposited conversion layer can be activelycontrolled by the switched-on duration of the LED chips during theelectrophoretic deposition, as a result of which the color locus canadvantageously be influenced in a targeted manner.

In one configuration of the method, an electrically insulating layer isapplied to the LED luminous unit before the first and/or secondconversion layer are/is applied by electrophoresis. The electricallyinsulating layer is structured using a radiation- and/or heat-sensitivelayer, wherein the radiation- and/or heat-sensitive layer is altered byradiation emitted by the portion of the LED chips and/or by generatedheat.

The electrically insulating layer is structured using a photoresistlayer, for example, wherein the photoresist layer is exposed by theradiation emitted by a portion of the LED chips.

By way of example, an electrically insulating layer is applied over thewhole area before the first and/or second conversion layer are/isapplied. A photoresist layer is subsequently applied to the electricallyinsulating layer, wherein the photoresist layer is exposed by theradiation of the LED chips of the subpixels onto which the first and/orsecond conversion layer are/is intended to be deposited. By way ofexample, openings are produced in the exposed regions of the photoresistlayer during development, which openings function as an etching mask toproduce openings in the electrically insulating layer above thesubpixels. The electrophoretic deposition thereupon takes place in theopenings of the electrically insulating layer above the subpixels whichwere electrically operated during exposure. The structured electricallyinsulating layer advantageously supports the selective deposition of thefirst and/or second conversion layer in the regions not covered by it.

The method described herein makes it possible to produce, in particular,an RGB LED display, wherein the first color is blue, the second color isgreen and the third color is red. The RGB LED display can contain inparticular blue-emitting LED chips, wherein the first conversion layerconverts the blue light into green light and the second conversion layerconverts the green and/or blue light into red light.

The method is particularly advantageously suitable for production of LEDdisplays having very small pixel sizes, wherein the pixels canpreferably have a width of less than 100 μm.

Our methods are explained in greater detail below on the basis ofexamples in association with FIGS. 1 to 10.

Identical or identically acting component parts are provided with thesame reference signs in the figures. The illustrated component parts andthe size relationships of the component parts among one another shouldnot be regarded as true to scale.

FIGS. 1A to 1F illustrate a first example of the method of producing amulticolor LED display.

As illustrated in FIG. 1A, the method involves providing an LED luminousunit 4 having a multiplicity of LED chips 3. The LED luminous unit 4 hasa plurality of pixels 5, wherein each pixel 5 has a plurality ofsubpixels R, G, B for emitting light of different colors. Preferably,each subpixel R, G, B contains an LED chip 3. The LEDs 3 which form thesubpixels R, G, B can be driven individually or at least in the groupsof the colors provided.

Each of the pixels 5 of the LED luminous unit 4 has three subpixels R,G, B, for example, that emit a first color, a second color and a thirdcolor. To simplify the illustration, FIG. 1A illustrates only two pixels5 each having three subpixels R, G, B, wherein the LED display actuallyhas a multiplicity of such pixels 5. The pixels 5 advantageously eachform an image point of the LED display and are preferably arranged in aplurality of lines and columns.

In this example and the examples described below, the multicolor LEDdisplay is an RGB LED display in which the first subpixels B emit bluelight, the second subpixels G emit green light and the third subpixels Remit red light. Here and hereinafter, the designations R, G, B of thesubpixels respectively symbolize the color which this subpixel emits inthe finished LED display. The designations R, G, B of the subpixels inparticular do not denote the color of the LEDs 3 which form thesubpixels. Rather, for all the subpixels identically colored LEDs 3which emit radiation of a first color, in particular blue light, arepreferably used in the LED luminous unit 4. The LED chips 3 can comprisenitride compound semiconductor materials, in particular.

To generate a second color and a third color with the LED chips 3 whichemit the first color, two conversion layers 1, 2 are used in the LEDdisplay.

As illustrated in FIG. 1B, in the example the conversion layers 1, 2 areapplied to the LED luminous unit 4 over the whole area. The firstconversion layer 1 and the second conversion layer 2 can comprise aceramic lamina, for example, into which a conversion substance isembedded. The first conversion layer 1 converts radiation of the firstcolor emitted by the LED chips 3 into radiation of a second color. Byway of example, the conversion layer 1 can convert blue light emitted bythe LED chips 3 into green light. In the example, the second conversionlayer 2 is arranged above the first conversion layer 1. In this case,the second conversion layer 2 is converts radiation of the second colorgenerated by the first conversion layer 1 into radiation of a thirdcolor. In particular, the second conversion layer 2 converts greenradiation generated from the blue radiation of the LED chips 3 by thefirst conversion layer 1 into red radiation. In one configuration, thesecond conversion layer 2 can also directly convert part of the blueradiation of the LED chips 3 into red radiation.

Suitable conversion substances that, for example, convert blue lightinto green light, blue light into red light, or green light into redlight, are known per se and will therefore not be explained in anygreater detail. Suitable matrix materials, in particular ceramics, intowhich the conversion substances to form a conversion layer 1, 2 can beembedded are likewise known per se and will therefore likewise not beexplained in any greater detail at this juncture.

If the LED luminous unit 4 were put into operation after the whole-areaapplication of the first conversion layer 1 and the second conversionlayer 2, all the subpixels R, G, B would emit red light on account ofthe two conversion layers 1, 2. In the method, therefore, as explainedin greater detail below, the second conversion layer 2 is removed fromthe second subpixels G and both the first conversion layer 1 and thesecond conversion layer 2 are removed from the third subpixels B. Forthis purpose, in the example in FIG. 1, a method of local layer removalis advantageously used, this method being controlled by a spectrallysensitive optical recognition of the radiation emitted by the LED chips3.

For this purpose, as illustrated in FIG. 1C, in a first step, the LEDchips of the second subpixels G and of the third subpixels B areelectrically operated, such that they emit radiation 6. The radiation 6emitted by the LED chips 3 is converted into red light on account of theconversion layers 1, 2. During operation of the subpixels B, G, thesecond conversion layer 2 is preferably locally removed by laserablation in the regions in which the radiation 6 is emitted. For thispurpose, a laser 7 is used, for example, which emits a laser beam 8whose wavelength is absorbed in the second conversion layer 2, whereinthe second conversion layer 2 is removed in this region by the laserbeam 8. A targeted positioning of the laser beam 8 onto a subpixel G tobe processed can advantageously be effected by optical image recognitionof the emitted radiation 6. The material removal by the laser radiation8 is effected until the second conversion layer 2 is completely removedin this region. This can be recognized from a change in color of theemitted radiation 6 from red to green. To automatically end the laserablation process at this point, a spectrally sensitive optical imagerecognition is advantageously used. In this way, the second conversionlayer 2 is sequentially removed for all second subpixels G and thirdsubpixels B of the LED display.

What is achieved in this way is that the second conversion layer 2, asillustrated in FIG. 1D, is substantially removed from the secondsubpixels G and the third subpixels B.

In a further method step, as illustrated in FIG. 1E, the firstconversion layer 1 is removed from the third subpixels B. For thispurpose, the LED chips 3 of the third subpixels B are electricallyoperated such that the latter emit green light 6 on account of the firstconversion layer 1 still present. As in the method step illustrated inFIG. 1C, material removal of the first conversion layer 1 is effected bylaser ablation, wherein the laser beam 8 of the laser 7 used for thematerial removal is controlled by a spectrally sensitive optical imagerecognition of the emitted radiation 6. In the method step in FIG. 1E, alaser 7 is advantageously used which emits radiation 8 having adifferent wavelength than the laser in the case of the method step inFIG. 1C. The material removal is effected, for example, until the blueprimary radiation of the LED chip 3 is emitted by the processed subpixelB. With the use of a spectrally sensitive optical image recognition, thematerial removal can advantageously be terminated in a targeted mannerat a point in time at which the emitted radiation 6 attains a desiredcolor locus. The method is carried out sequentially for all thirdsubpixels B until the latter in each case emit blue radiation 6 having adesired color locus.

In this way, the multicolor LED display 10 illustrated in FIG. 1F isproduced, the display having a plurality of pixels 5, wherein the pixels5 have three subpixels R, G, B. The first subpixels B emit non-convertedlight of the LED chips 3, in particular blue light. The second subpixelsG emit light of the second color converted by the first conversion layer1, in particular green light. The third subpixels R emit light of thethird color converted by the first conversion layer 1 and the secondconversion layer 2, in particular red light.

FIGS. 2A to 2F illustrate a further example of the method wherein thefirst conversion layer 1 and the second conversion layer 2 are removedfrom a portion of the subpixels G, B by a method of local layer removal.

As in the example in FIG. 1, in the intermediate step of the method asillustrated in FIG. 2A, the first conversion layer 1 and the secondconversion layer 2 have been applied to the LED luminous unit 4 over thewhole area. In addition, a preferably liquid etchant 11 has been appliedto the second conversion layer 2. The etchant 11 is preferably appliedat a temperature at which the etching rate of the etchant is negligiblylow. This can take place, for example, at room temperature or in acooled environment, wherein the etching rate of the etchant 11 at roomtemperature or in the cooled environment is negligibly low. Thetemperature of the applied etchant can alternatively be higher than roomtemperature, provided that the etching rate of the etchant at thistemperature is negligibly low.

In the intermediate step illustrated in FIG. 2B, the LED chips 3 of thesecond subpixels G and of the first subpixels B, from which the secondconversion layer 2 is intended to be removed, are thereupon electricallyoperated. By virtue of the heat generated by the LED chips 3 of thesubpixels G, B, the etchant 11 heats up to a great extent locally abovethe subpixels G, B such that the etching rate rises there and leads to alocal removal of the second conversion layer 2 in these regions.

Alternatively or additionally, the etching rate can be locally increasedby the radiation 6 emitted by the subpixels G, B. A so-calledphoto-assisted etching process is involved in this case.

In this example of the method, the layer removal advantageously takesplace from all electrically operated subpixels G, B simultaneously. Asin the first example, the layer removal process can be controlled overtime by a spectrally sensitive optical image recognition, wherein theetching process is terminated if no longer red light but ratherpredominantly green light is emitted in the regions of the subpixels G,B. The etching process can be terminated by the subpixels G, B beingswitched off by the application of a neutralization agent and/or byrinsing.

What is achieved in this way is that the second conversion layer 2 isremoved from the subpixels G, B, as illustrated in FIG. 2C.

Afterward, as illustrated in FIG. 2D, a further preferably liquidetchant 12, that selectively etches the first conversion layer 1, isapplied preferably at room temperature or in a cooled environment. Likethe first etchant 11 used previously, the second etchant 12, too, isadvantageously applied at a temperature at which the etching rate of theetchant is negligibly low.

As illustrated in FIG. 2E, subsequently, the LED chips 3 of the firstsubpixels B are electrically operated, wherein, as a result of the localevolution of heat, the etching rate rises to a great extent above thesubpixels B and thus leads to removal of the first conversion layer 1.As in the intermediate step illustrated in FIG. 2B, the etching processcan be controlled by spectrally sensitive optical image recognition,wherein the etching process is preferably terminated if the color of theemitted radiation has changed from green to blue.

The multicolor LED display 10 completed in this way is illustrated inFIG. 2F and corresponds to the LED display illustrated in FIG. 1F.

A further example of the method is illustrated in FIGS. 3A to 3F. Thisexample is a modification of the example illustrated in FIGS. 2A to 2Fwherein a local layer removal of the first conversion layer 1 and of thesecond conversion layer 2 is effected by etchants 11, 12. As illustratedin FIG. 3A, however, the first etchant 11 is not applied to the secondconversion layer 2 over the whole area, but rather locally above thesubpixels G, B above which the second conversion layer 2 is intended tobe removed. The local application of the etchant 11 can be effected byan inkjet method, for example. In this configuration, the LED chips 3 ofthe second subpixels G and of the third subpixels B are advantageouslyelectrically operated during the application of the etchant 11 such thatthe local application can advantageously be controlled by optical imagerecognition of the emitted radiation 6.

As in the previous example in FIG. 2, the local layer removal of thesecond conversion layer 2 illustrated in FIG. 3B can be effected underthe influence of the heat and/or radiation generated during theoperation of the LED chips 3 of the subpixels G, B. In contrast to theexample in FIG. 2, the local application of the etchant 11 enablescontrol of the etching process, in particular termination at a desiredpoint in time, by an accurate apportioning of the etchant 11. A controlof the etching process by emitted heat and/or radiation is therefore notabsolutely necessary. It is also possible for small amounts of theetchant 11 to be applied repeatedly, for example, to set the color locusof the subpixels G, B in a targeted manner. In an etching rate greatlyincreased by heat, the etching process can be ended by the subpixels G,B being switched off. Alternatively, the etching process can beterminated by rinsing or application of a neutralization agent after adesired etching depth and/or a desired color locus have/has beenattained.

In this way, in particular, as illustrated in FIG. 3C, the secondconversion layer 2 can be removed from the second subpixels G and thefirst subpixels B.

As illustrated in FIG. 3D, the method is continued correspondingly witha second etchant 12, that etches the first conversion layer 1. Thesecond etchant 12 is locally applied to the first subpixels B, whereinthe local application can be effected by an inkjet method and can besupported by an optical image recognition of the radiation 6 emitted bythe LED chips 3 of the first subpixels B.

Afterward, as illustrated in FIG. 3E, the local layer removal of thesecond conversion layer 2 is effected by the second etchant 12.

In this way, the multicolor LED display 10 illustrated in FIG. 3F isproduced, which corresponds to the examples in FIGS. 1F and 2F.

A further example of the method wherein a local layer removal of thefirst conversion layer 1 and of the second conversion layer 2 iseffected is illustrated in FIGS. 4A to 4E.

As in the previous examples, after the application of the conversionlayers 1, 2 as illustrated in FIG. 4A, first a local layer removal ofthe second conversion layer 2 is effected, which is illustrated in FIG.4B. The LED chips 3 of the first and second subpixels B, G, from whichthe second conversion layer 2 is removed, are electrically operated inthis process step. The layer removal is effected by a dry etchingprocess, symbolized by the arrows 9. In this variant of the method, alocally amplified etching of the second conversion layer above theelectrically operated subpixels G, B is obtained by the electric fieldgenerated during the operation of the LED chips 3 of the subpixels B, G.Furthermore, the heat generated by the LED chips 3 during operation canlocally amplify the dry etching process.

In this way, as illustrated in FIG. 4C, first the second conversionlayer 2 is removed from the second subpixels G and the first subpixelsB.

In a further step, illustrated in FIG. 4D, only the first subpixels Bare electrically operated, wherein the first conversion layer 1 isselectively removed from the first subpixels B by a further dry etchingprocess 9. The locally amplified etching rate above the subpixels B isonce again brought about by the electric field generated by the LEDchips 3 of the subpixels B and by the locally emitted heat.

In this way, the multicolor LED display 10 illustrated in FIG. 4E isproduced, which corresponds to the multicolor LED displays of theprevious examples.

A further example of the method is illustrated in FIGS. 5A to 5H. Asillustrated in FIG. 5A, in this example, first a first photoresist layer13 is applied to the LED luminous unit 4. The first photoresist layer 13can be applied by spin-coating, for example. The photoresist layer 13 issubsequently exposed by radiation emitted by the LED chips 3 of thesecond subpixels G. This process can analogously also be brought aboutby the heat that arises locally during operation of a portion of the LEDchips 3 or by an interaction of the emitted electromagnetic radiationand the emitted heat, if a heat-sensitive polymer is used as thephotoresist layer or instead of the photoresist layer.

In the method step illustrated in FIG. 5B, development of thephotoresist layer 13 produces openings 15 above the subpixels G whoseLED chips 3 were operated during the exposure of the photoresist layer13.

In a further method step illustrated in FIG. 5C, the first conversionlayer 1 is applied to the structured photoresist layer 13. The firstconversion layer 1 is subsequently removed again together with thephotoresist layer 13 outside the openings produced previously.

As illustrated in FIG. 5D, after lift-off of the photoresist layer 13,regions of the first conversion layer 1 remain above the subpixels Gwhose LED chips 3 were used previously to expose the photoresist layer13.

The previous method steps can subsequently be repeated correspondinglyto apply a second conversion layer 2. In this regard, in the method stepillustrated in FIG. 5E, a second photoresist layer 14 is applied to thestructured first conversion layer 1 produced previously and is exposedby the radiation 6 from the LED chips 3 of the subpixels R to which thesecond conversion layer is intended to be applied.

In the method step illustrated in FIG. 5F, development of the secondphotoresist layer 14 produces openings 15 in the exposed regions abovethe third subpixels R.

In the intermediate step illustrated in FIG. 5G, the second conversionlayer 2 is applied to the second photoresist layer 14 thus structured.In the example, the second conversion layer 2 converts the radiation ofthe first color of the LED chips, for example, blue light, intoradiation of the third color, for example, red light.

After the second conversion layer 2 has been applied, the secondphotoresist layer 14 is removed by lift-off technology including theregions of the second conversion layer 2 arranged thereabove.

After this method step has been carried out, as illustrated in FIG. 5H,regions of the second conversion layer 2 remain above the thirdsubpixels R used previously to expose the second photoresist layer 14.In the multicolor LED display 10 produced in this way, the firstconversion layer 1 is arranged above the second subpixels G such thatthe second subpixels G emit the converted radiation of the second color,in particular green light. The second conversion layer 2 is arrangedabove the third subpixels R such that the third subpixels R emitradiation of the third color, in particular red light.

Alternatively, in the example in FIG. 5, it would also be possible as inthe previous examples to use a second conversion layer 2 that convertsradiation of the second color, for example, green light, into radiationof the third color, for example, red light. In this case, in the methodsteps in FIGS. 5A to 5D, the first conversion layer 1 would be appliedabove the second and third subpixels R, G and, in the method steps inFIGS. 5E to 5H, the second conversion layer 2 would be applied above thefirst conversion layer 1 of the third subpixels R.

In the method illustrated in FIGS. 5A to 5H, the photoresist layers 13,14 used were positive photoresist layers in which openings 15 ariseduring development in the exposed regions. Alternatively, it would alsobe possible to use negative resist layers as photoresist layers 13, 14in which openings are produced in the non-exposed regions duringdevelopment. Accordingly, in this variant of the method (notillustrated), in the method step illustrated in FIG. 5A the subpixels R,B above which a first conversion layer is not intended to be depositedwould have to be electrically operated. Furthermore, in the method stepillustrated in FIG. 5E the subpixels G, B above which the secondconversion layer 2 is not intended to be deposited would have to beelectrically operated. The remaining method steps, with the use ofnegative resist layers, correspond to the intermediate steps of theexample illustrated in FIG. 5.

A further example of the method of producing a multicolor LED display isillustrated in FIGS. 6A to 6F.

In the method step illustrated in FIG. 6A, a first conversion substance16 in a dispersion 18 is applied to the LED luminous unit 4. The firstconversion substance 16 is, for example, a conversion substance thatconverts blue light emitted by the LED chips 3 into green light. Thefirst conversion substance 16 is deposited onto the subpixels G in theform of a first conversion layer.

The targeted deposition of the conversion substance 16 on the subpixelsG is effected as illustrated in FIG. 6B by an electrophoretic depositionin which the LED chips 3 of the subpixels G are electrically operated.During operation, the LED chips 3 of the subpixels G generate anelectric field which brings about a deposition of the conversionsubstance 16 on the subpixels G.

Afterward, a drying step and preferably a baking step take place to formthe first conversion layer 1 above the subpixels G from the conversionsubstance 16 deposited in the dispersion 18, as is illustrated in FIG.6C.

As illustrated in FIG. 6D, a second dispersion 19 containing a secondconversion substance 17 is subsequently applied. The second conversionsubstance 17, for example, converts the blue radiation emitted by theLED chips 3 into red light.

As illustrated in FIG. 6E, the second conversion substance 17 isdeposited electrophoretically above the subpixels R by virtue of the LEDchips 3 of the subpixels R being electrically operated and in this waygenerating an electric field which leads to the deposition of the secondconversion substance 17 above the subpixels R.

After a further drying process and preferably a further baking process,the multicolor LED display 10 illustrated in FIG. 6F is produced, inwhich the first conversion layer 1 that converts blue light into greenlight is arranged above the second subpixels G and the second conversionlayer 2 that converts blue light into red light is arranged above thethird subpixels R. As in the example in FIG. 5, in this example thesecond conversion layer 2 directly converts blue light into red light.Alternatively, however, it would also be possible to apply to the thirdsubpixels R a first conversion layer 1 which converts blue light intogreen light, and to apply thereto the second conversion layer 2 whichconverts green light into red light.

FIGS. 7A to 7J illustrate a further example of the method, this being amodification of the example of the method as illustrated in FIG. 6.

In the first method step of the example as illustrated in FIG. 7A, anelectrically insulating layer 20 is applied to the LED luminous unit 4.The electrically insulating layer 20 can be in particular an oxide ornitride layer, for example, a silicon oxide layer. The insulating layer20 can be a protective passivation which is usually a constituent partof the LED chips 3. It is also possible for at least one further layer,for example, a layer composed of a transparent conductive oxide, to besituated between the LED chips 3 and the insulating layer 20.

In a further method step illustrated in FIG. 7B, a photoresist layer 13is applied to the electrically insulating layer 20 and exposed by theradiation 6 emitted by the LED chips 3 of the second and third subpixelsR, G.

As illustrated in FIG. 7C, the photoresist layer 13 is subsequentlydeveloped and openings 15 are thereby produced above the subpixels R, Gwhich were electrically operated during exposure. As an alternative tothe method steps in FIGS. 7A to 7C, it would also be possible to producethe openings 15 above the second and third subpixels R, G in separatemethod steps.

The photoresist layer 13 structured in this way is used as an etchingmask for structuring the underlying electrically insulating layer 20.

In this way, as illustrated in FIG. 7D, a structured electricallyinsulating layer 20 is produced which has openings 15 above the secondand third subpixels R, G, above which a conversion layer is intended tobe deposited.

The further method steps illustrated in FIGS. 7E to 7J correspond to themethod steps of the previous example as illustrated in FIGS. 6A to 6F,with the difference that the structured electrically insulating layer 20is situated on the LED luminous unit 4.

The first conversion layer 1 and the second conversion layer 2 aredeposited above the subpixels R, G by electrophoretic deposition as inthe example in FIG. 6. During the electrophoretic deposition of thefirst conversion substance 16 above the second subpixels G, which isillustrated in FIG. 7F, and the electrophoretic deposition of the secondconversion substance 17 above the third subpixels R, which isillustrated in FIG. 71, the advantage of the structured electricallyinsulating layer 20 applied previously is that the electrophoreticdeposition above the electrically conductive material of the subpixelsR, G is promoted compared to the regions of the electrically insulatinglayer 20. The surfaces of the subpixels R, G can be formed in particularby the electrically conductive material of the LED chips 3 which formthe subpixels R, G.

The remaining method steps of the example in FIG. 7 correspond to theexample illustrated in FIG. 6 and will therefore not be explained again.

A further example is illustrated in FIGS. 8A to 8I. As illustrated inFIG. 8A, in the example in a first step the conversion layers 1, 2 areapplied to the LED luminous unit 4 over the whole area. A radiation-and/or heat-sensitive layer 21 is applied to the second conversion layer2.

As illustrated in FIG. 8B, the radiation- and/or heat-sensitive layer 21is subjected to the action of the heat and/or radiation 6 emitted by theLED chips 3 of the first subpixels B.

The radiation- and/or heat-sensitive layer 21 is subsequentlystructured, for example, by a development process such that it hasopenings 15 above the first subpixels B as illustrated in FIG. 8C.

The radiation- and/or heat-sensitive layer 21 structured in this way issubsequently used as an etching mask for a wet-chemical or dry etchingprocess. In this way, the first conversion layer 1 and the secondconversion layer 2 are removed above the first subpixels B, asillustrated in FIG. 8D.

In a further step illustrated in FIG. 8E, the radiation- and/orheat-sensitive layer 21 is removed again.

In the method step illustrated in FIG. 8F, a further radiation- and/orheat-sensitive layer 22 has been applied, which covers the first andsecond conversion layers 1, 2 and the first subpixels B previouslyuncovered. The LED chips 3 of the second subpixels G are subsequentlyelectrically operated such that the further radiation- and/orheat-sensitive layer 22 is subjected to the action of the heat and/orradiation 6 emitted by the LED chips 3 of the second subpixels G. Theradiation- and/or heat-sensitive layer 22 is subsequently structured,for example, by a development process such that it has openings 15 abovethe second subpixels G, as illustrated in FIG. 8G.

The radiation- and/or heat-sensitive layer 22 structured in this way issubsequently used as an etching mask for a wet-chemical or dry etchingprocess. By the etching process, the second conversion layer 2 isremoved above the second subpixels G, as illustrated in FIG. 8H.

In a further step, illustrated in FIG. 8I, the further radiation- and/orheat-sensitive layer 22 is removed again. The multicolor LED display 10completed in this way corresponds to the LED display illustrated in FIG.1F.

In a modification of the example in FIG. 8, instead of the applicationof the radiation- and/or heat-sensitive layer 21 illustrated in FIG. 8A,a radiation-absorbing layer 23 is applied, as illustrated in FIG. 9. Aheat-sensitive layer 24 is applied to the radiation-absorbing layer 23.The radiation-absorbing layer 23 has the function, in particular, ofconverting the radiation 6 emitted by the operated LED chips 3 into heatsuch that the heat acts on the heat-sensitive layer 24. A layer sequencecomprising a radiation-absorbing layer 23 and a heat-sensitive layer 24can also be applied instead of the second radiation- and/orheat-sensitive layer in the further course of the method. The remainingmethod steps can be carried out analogously to the example in FIG. 8 andwill therefore not be explained in greater detail again.

A layer sequence comprising a radiation-absorbing layer 23 and aheat-sensitive layer 24 can also be used instead of the photoresistlayer in the above-described example in FIG. 5. In this case, the methodstep in FIG. 5A is replaced by the method step illustrated in FIG. 10 inwhich the radiation-absorbing layer 23 and the heat-sensitive layer 24are applied to the LED luminous unit 4. A layer sequence comprising aradiation-absorbing layer 23 and a heat-sensitive layer 24 can also beapplied instead of the second photoresist layer 14 in the further courseof the method. The remaining method steps can be carried out analogouslyto the example in FIG. 5 and will therefore not be explained in greaterdetail again.

In all of the examples described above it is possible to apply atransparent protective layer, for example, composed of SiO₂ to theapplied conversion layers 1, 2. The transparent protective layer ispreferably applied to the multicolor LED display over the whole area.

In the examples described above, the method of producing the multicolorLED display was explained on the basis of the example of an RGB LEDdisplay. However, the multicolor LED display can also have other colorcombinations, in particular with more than three colors. It is alsopossible to use more than two conversion layers to generate theplurality of colors in the multicolor LED display.

Our methods are not restricted by the description on the basis of theexamples. Rather, the disclosure encompasses any novel feature and alsoany combination of features, which in particular includes anycombination of features in the appended claims, even if the feature orcombination itself is not explicitly specified in the claims orexamples.

The invention claimed is:
 1. A method of producing a multicolor LED(light emitting diode) display comprising an LED luminous unit having amultiplicity of pixels, wherein: the pixels comprise first subpixelsthat emit a first color, second subpixels that emit a second color andthird subpixels that emit a third color, the subpixels contain an LEDchip that emits radiation of the first color, a first conversion layerthat converts radiation of the first color into radiation of the secondcolor is arranged at least above the second subpixels, and a secondconversion layer that converts radiation of the first color and/or theradiation of the second color into radiation of the third color isarranged above the third subpixels, comprising: implementing at leastone process step in which the first conversion layer or the secondconversion layer is applied or removed in at least one defined regionabove the pixels to arrange the first conversion layer above the secondsubpixels and arrange the second conversion layer above the thirdsubpixels, electrically operating in the process step a portion of theLED chips, and defining at least one region by electromagnetic radiationgenerated by the portion of the LED chips, generated heat or a generatedelectric field, wherein: a radiation- and/or heat-sensitive layer isapplied and altered in regions by the radiation emitted by the portionof the LED chips and/or by the generated heat, and in the regions oroutside the regions openings are produced in the radiation- and/orheat-sensitive layer.
 2. The method according to claim 1, wherein theradiation- and/or heat-sensitive layer is a photoresist layer and thephotoresist layer is exposed in the regions by the electromagneticradiation emitted by the portion of the LED chips.
 3. The methodaccording to claim 1, wherein the radiation- and/or heat-sensitive layeris a heat-sensitive layer, and the heat sensitive layer is altered inthe regions by the heat generated by the portion of the LED chips. 4.The method according to claim 3, wherein a radiation-absorbing layer isapplied before the heat-sensitive layer is applied.
 5. The methodaccording to claim 1, wherein the first conversion layer or the secondconversion layer is applied to the radiation- and/or heat-sensitivelayer and is removed again outside the openings by lift-off technology.6. The method according to claim 1, wherein the radiation- and/orheat-sensitive layer is applied to the first conversion layer or to thesecond conversion layer, and the first conversion layer or the secondconversion layer is removed in the openings by a method of layerremoval.
 7. The method according to claim 6, wherein the method of layerremoval is an etching process.
 8. The method according to claim 7,wherein an electrically insulating layer is applied before the firstand/or second conversion layer are/is applied, said electricallyinsulating layer being structured using a radiation- and/or heat-sensitive layer, and the radiation- and/or heat-sensitive layer isaltered by the radiation generated by the portion of the LED chipsand/or by the generated heat.
 9. The method according to claim 8,wherein the radiation- and/or heat-sensitive layer is a photoresistlayer and the photoresist layer is exposed by the electromagneticradiation emitted by the portion of the LED chips.
 10. The methodaccording to claim 1, wherein the radiation- and/or heat sensitive layeris removed again after applying the first conversion layer and/or thesecond conversion layer.
 11. A method of producing a multicolor LED(light emitting diode) display comprising an LED luminous unit having amultiplicity of pixels, wherein: the pixels comprise first subpixelsthat emit a first color, second subpixels that emit a second color andthird subpixels that emit a third color, the subpixels contain an LEDchip that emits radiation of the first color, a first conversion layerthat converts radiation of the first color into radiation of the secondcolor is arranged at least above 1) the second subpixels and 2) abovethe LED luminous unit, and a second conversion layer that convertsradiation of the first color and/or the radiation of the second colorinto radiation of the third color is arranged above 1) the thirdsubpixels and 2) the first conversion layer, comprising: implementing atleast one process step in which the first conversion layer or the secondconversion layer is applied or removed in at least one defined regionabove the pixels to arrange the first conversion layer above the secondsubpixels and arrange the second conversion layer above the thirdsubpixels, electrically operating in the process step a portion of theLED chips, and defining at least one region by electromagnetic radiationgenerated by the portion of the LED chips, generated heat or a generatedelectric field, wherein: the second conversion layer is removed from thefirst subpixels and the second subpixels, and the first conversion layeris removed from the first subpixels, and removal of the first conversionlayer and/or of the second conversion layer is effected by a method oflocal layer removal locally amplified by heat emitted by the portion ofthe LED chips and/or by electromagnetic radiation emitted by the portionof the LED chips.
 12. The method according to claim 1, wherein removalof the first conversion layer and/or of the second conversion layer iseffected by a method of local layer removal controlled by a spectrallysensitive optical recognition of the electromagnetic radiation emittedby the portion of the LED chips.
 13. The method according to claim 12,wherein the method of local layer removal is laser ablation or anetching process.
 14. The method according to claim 1, wherein the methodof local layer removal is a wet-chemical etching method.
 15. The methodaccording to claim 1, wherein the removal of the first conversion layerand/or of the second conversion layer is effected by a method of locallayer removal locally amplified by the electric field generated by theportion of the LED chips.
 16. The method according to claim 15, whereinthe method of local layer removal is a dry etching method.
 17. Themethod according to claim 11, wherein the first conversion layer and/orthe second conversion layer are/is deposited by electrophoresis, and thedeposition is locally amplified by the electric field generated by theportion of the LED chips.
 18. The method according to claim 11, whereinthe pixels have a width of less than 100 μm.